This invention relates to motors. In particular, this invention relates to a non-pollution motor powered from a supply of a liquified cryogenic, such as liquid nitrogen, which is maintained at its cryogenic temperature. The liquified cryogenic is expanded to obtain a high pressure gas that provides the energy needed to power the motor. The high pressure gas is vented to atmosphere without adding any pollutants to the air.
Non-pullution motors powered from a supply of a liquified cryogenic are known in the art. U.S. Pat. Nos. 3,681,609, 3,842,333, and 3,870,942, each issued to the applicant of the present application as a joint patentee, disclose the use of a liquidfied cryogenic as the power source for a non-pullution motor. The liquified cryogenic is maintained at a high pressure due to the expansion of some of the cryogenic from its liquid to its gaseous state. This high pressure gas is used to power a gas turbine motor which, in turn, powers a DC-generator. The power from the generator is stored in batteries. The batteries are used to power a DC-motor which provides the output drive for the non-pullution motor.
To achieve performance characteristics from both the DC-generator and DC-drive motor that exceed their normal ratings, it is important to cool both units to as low a temperature as possible. U.S. Pat. Nos. 3,842,333 and 3,870,942 disclose two different approaches to this requirement. First, U.S. Pat. No. 3,842,333 shows passing the liquified gas through tubes that pass around the drive motor housing in heat exchange relationship to achieve cooling of the motor. Second, U.S. No. 3,870,942 discloses that the liquified cryogenic can be passed through both the DC-generator and the DC-drive motor. In the cooling system of U.S. Pat. No. 3,842,333, only a minimum efficiency in cooling is achieved. In the cooling system of U.S. Pat. No. 3,870,942, a greater efficiency is achieved, but at a loss in performance due to the presence of the fluid in the moving parts of the units.
Another problem present in these prior-art motors is the excessive loss of high pressure gas through evaporation of the liquified cryogenic in the cryogenic tank. The rate of evaporation of the pressurized liquid cryogenic is directly related to the pressure. The higher the pressure, the greater the rate of evaporation. For the non-pollution motor disclosed in the above references, the pressure, beginning at the source of liquified cryogenic up thru the gas motor, is maintained at the same high pressure level. Since the liquified cryogenic is at a high pressure, excessive evaporation of the cryogenic in the cryogenic tank results.
Accordingly, it would be advantageous to provide a non-pollution motor that minimizes the rate of evaporation of a liquified cryogenic by substantially reducing its operating pressure while maintaining a high pressure gas supply for use in the gas motor. It would also be advantageous to achieve a significant improvement in the performance characteristics from both the generator and the drive motor by cooling them to essentially the same cryogenic temperature as the temperaure of the liquified cryogenic without direct contact between the cryogenic and the units.